Plasmodium falciparum, plasmodium vivax, plasmodium ovale, and plasmodium milariae are known types of malaria. Among these, plasmodium falciparum malaria is likely to become severe in humans, and those infected require prompt medical treatment. Methods of diagnosing those infected by malaria include, for example, the method described in Japanese laid-open patent No. 2007-24844. In this method, a measurement sample is prepared by adding reagent for lysing red blood cells to a blood sample. Optical information is obtained when the prepared measurement sample is irradiated with light, and the presence or absence of malaria parasites in the measurement sample is determined based on the obtained optical information. In this case, malaria parasites and white blood cells are discriminated using a white blood cell detection scattergram.
Among these four types of malaria, the malaria parasites of plasmodium falciparum often form a ring formation in red blood cells. The malaria parasites of the ring formation cannot be detected by the method disclosed in Japanese laid-open patent No. 2007-24844 because the size is smaller than the red blood cells.